4. (15 points) A gas turbine aircraft engine has blades made out of S-590 alloy. The most critical row of blades has stress (bending + axial) and temperature T that vary with location according to the figure below, where x is the distance beyond the base of the blade. These values correspond to the most severe operating condition encountered in the normal use of the aircraft. The S-590 alloy is assumed to obey the Larson-Miller(LM) creep rupture equation. Stress vs. LM Parameter curve is also given below. a) Estimate the life of the blades, as limited by creep- rupture? b) The maintenance schedule specifies replacing these blades every 5000 flight hours. What is the factor of safety in stress is provided by this retirement life? c) What safety margin in temperature is provided by the 5000 hour retirement life? d) Do you agree with the 5000-hour retirement life? Should it be shorter or longer? , Stress, MPa 20 C-17 log(hours) 400 OOD DO 20,000 PLM-Larson-Miller Parameter, K-log(hours) 24,000 956 888 20 , ksi 00 S-590 a go 88